Morphologie der Seeigelzähne

The teeth of sea-urchins are not to be compared with the other skeletal-structures of echinoderms. The tooth is constructed of two rows of calcitelements, which are connected by secondary calcareous deposits forming the functional tooth. The surface of the tooth is covered by a crust of calcit. This fundamental construction is described from Stylocidaris affinis, which belongs to the archaic Cidaridae.

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Verzeichnis der benutzten Signaturen aO apikaler Odontoblastenherd - BG Basalgeflecht - F Flügel - H Haftrinde - HF Hauptfalte - HP Haftpunkt - K Kante - KA Kauabschnitt - KK Kaukante - L Lamellen - LB Lithoblasten - lP laterale Prismen - M Medianebene - MR Medianrinne - N Nadeln - NF Nebenfalte - P Prismen - PB prismenbildende Zellen - Pl Plumula - PP Primärplatte - PZ Plattenzähne - QF Querfalte - R Rinde - Ri Kalkrippen - Sch Schaft - sO subapikale Odontoblasten - SP Sekundärplatte - ST Steinteil - U Umbo - ZB Zellblätter - zP zentrale Prismen Mit Unterstützung der Deutschen Forschungsgemeinschaft (Beihilfe an den erstgenannten Autor).     

The giant oyster Hyotissa hyotis from the northern Red Sea as a decadal-scale archive for seasonal environmental fluctuations in coral reef habitats

This study explores the giant oyster Hyotissa hyotis as a novel environmental archive in tropical reef environments of the Indo-Pacific. The species is a typical accessory component in coral reefs, can reach sizes of tens of centimetres, and dates back to the Late Pleistocene. Here, a 70.2-mm-long oxygen and carbon isotope transect through the shell of a specimen collected at Safaga Bay, northern Red Sea, in May 1996, is presented. The transect runs perpendicularly to the foliate and vesicular layers of the inner ostracum near the ligament area of the oyster. The measured δ¹⁸O and δ¹³C records show sinusoidal fluctuations, which are independent of shell microstructure. The δ¹³C fluctuations exhibit the same wavelength as the δ¹⁸O fluctuations but are phase shifted. The δ¹⁸O record reflects the sea surface temperature variations from 1957 until 1996, possibly additionally influenced by the local evaporation. Due to locally enhanced evaporation in the semi-enclosed Safaga Bay, the δ¹⁸O_seawater value is estimated at 2.17‰, i.e., 0.3–0.8‰ higher than published open surface water δ¹⁸O values (1.36–1.85‰) from the region. The mean water temperature deviates by only 0.4°C from the expected value, and the minimum and maximum values are 0.5°C lower and 2.9°C higher, respectively. When comparing the mean monthly values, however, the sea surface temperature discrepancy between reconstructed and global grid datasets is always <1.0°C. The δ¹³C signal is weakly negatively correlated with regional chlorophyll a concentration and with the sunshine duration, which may reflect changes in the bivalve’s respiration. The study emphasises the palaeogeographic context in isotope studies based on fossils, because coastal embayments might not reflect open-water oceanographic conditions.     

Solenosmilia variabilis-bearing cold-water coral mounds off Brazil

Coral Reefs - Cold-water corals (CWC), dominantly Desmophyllum pertusum (previously Lophelia pertusa), and their mounds have been in the focus of marine research during the last two decades;...     

Linking sedimentary sulfur and iron biogeochemistry to growth patterns of a cold‐water coral mound in the Porcupine Basin,S.W. Ireland (IODP Expedition 307)

Challenger Mound, a 150‐m‐high cold‐water coral mound on the eastern flank of the Porcupine Seabight off SW Ireland, was drilled during Expedition 307 of the Integrated Ocean Drilling Program (IODP). Retrieved cores offer unique insight into an archive of Quaternary paleo‐environmental change, long‐term coral mound development, and the diagenetic alteration of these carbonate fabrics over time. To characterize biogeochemical carbon–iron–sulfur transformations in the mound sediments, the contents of dithionite‐ and HCl‐extractable iron phases, iron monosulfide and pyrite, and acid‐extractable calcium, magnesium, manganese, and strontium were determined. Additionally, the stable isotopic compositions of pore‐water sulfate and solid‐phase reduced sulfur compounds were analyzed. Sulfate penetrated through the mound sequence and into the underlying Miocene sediments, where a sulfate–methane transition zone was identified. Small sulfate concentration decreases (<7 mm ) within the top 40 m of the mound suggested slow net rates of present‐day organoclastic sulfate reduction. Increasing δ³⁴S‐sulfate values due to microbial sulfate reduction mirrored the decrease in sulfate concentrations. This process was accompanied by oxygen isotope exchange with water that was indicated by increasing δ¹⁸O‐sulfate values, reaching equilibrium with pore‐water at depth. Below 50 mbsf, sediment intervals with strong ³⁴S‐enriched imprints on chromium‐reducible sulfur (pyrite S), high degree‐of‐pyritization values, and semi‐lithified diagenetic carbonate‐rich layers characterized by poor coral preservation, were observed. These layers provided evidence for the occurrence of enhanced microbial sulfate‐reducing activity in the mound in the past during periods of rapid mound aggradation and subsequent intervals of non‐deposition or erosion when geochemical fronts remained stationary. During these periods, especially during the Early Pleistocene, elevated sulfate reduction rates facilitated the consumption of reducible iron oxide phases, coral dissolution, and the subsequent formation of carbonate cements.     

From sediment to rock: diagenetic processes of hardground formation in deep-water carbonate mounds of the NE Atlantic

Modern cool-water carbonate mounds topped by corals form an extended reef belt along the NW European continental margin at 200–1200 m water depth. An essential element of mound growth are hardgrounds which provide a stable substratum for mound-building invertebrate colonisation and stabilise the inclined mound flanks. Evaluating the degree of lithification and the slope stability against erosion represents an important task within the ESF programme MOUNDFORCE under the umbrella of EUROMARGINS. Sampling of hardgrounds during RV Meteor cruises M61-1 and -3 in 2004 by means of the IFM-GEOMAR TV-grab and the Bremen ROV QUEST focused on carbonate mounds of the Porcupine Seabight and northwestern Rockall Bank off Ireland. Lithified carbonates of mid-Pleistocene age were exhumed during the Holocene and are now exposed on the top and flanks of numerous carbonate mounds showing a patchy to dense colonisation by living corals and associated invertebrates. The sediments, composed of foraminiferal–nannoplankton oozes and admixed mound-derived invertebrate skeletons, range from partly lithified chalks to dense micritic limestones. These wackestones to packstones clearly differ from bacterially induced authigenic carbonate crusts typical of hydrocarbon seep settings by showing current-induced sedimentary structures, a non-luminescing matrix indicating oxic pore fluids, and a marine isotopic signature lacking any depleted carbon regime which is typical of anaerobic methane oxidation. The carbonate lithification is driven by carbonate ion diffusion from supersaturated seawater into the pore fluids in the studied areas. Vigorous bottom currents were the ultimate control not only of carbonate cementation by enhancing the diffusion process and supporting a pumping mechanism, but also of hardground formation and mound shaping by exhuming lithified carbonates and preventing fine-grained sediment accumulation at the downslope mound flanks.